The present invention relates to valves in general, especially to shutoff valves for pressurized fluids, and more particularly to improvements in valves with plunger type solenoids. Still more particularly, the invention relates to improvements in valves wherein the plunger of the solenoid directly cooperates with a fixed valve seat.
It is often necessary to establish or interrupt the flow of a pressurized fluid (particularly a compressed gas) at frequent intervals. Solenoid operated valves are highly suitable for such purposes and have found widespread use in many fields where the flow of pressurized gas must be controlled at intervals as frequent as several thousand times per minutes. Typical examples of applications of such valves are in testing of cigarettes or analogous rod-shaped products which are produced in quantities of up to and in excess of 70 per second and are monitored, one after the other, for the quality of their wrappers, density of their tobacco-containing ends, presence or absence of printed matter and/or other characteristics. Defective articles must be segregated from satisfactory articles with a high degree of reliability in order to prevent defective articles from reaching the consumer. This entails rapid opening of a valve which discharges compressed gas (normally air) when a defective or potentially defective article reaches the segregating station, and the valve must close practically instantaneously to avoid ejection of one or more satisfactory articles which follow a defective article. By the same token, the valve should not open prematurely in order to avoid segregation of one or more satisfactory articles preceding a defective article which is on its way to the ejecting station. The situation is analogous in many other fields, for example, in connection with electronic monitoring of the quality, size and/or other characteristics of coffee beans or other discrete commodities.
Attempts to enable presently known solenoid operated valves to satisfy the requirements in the just-enumerated and other fields have met with limited success. For example, it was already proposed to employ springs and/or other biasing means to accelerate the movements of the armature of a solenoid operated valve to the one (closing) or the other (open) position. Resilient means can promote rapid movement of the armature to one end position (e.g., to closed position); however, they oppose the movement of the armature to the other end position so that they actually delay the opening of the valve. Other known proposals, mainly attempts to achieve a compromise between predictable closing and opening of the valve, failed to gain acceptance in many industries because the frequency at which such valves open or close is too low.